1. (Field of the Invention)
The present invention relates to activated clay for treating aromatic hydrocarbons. More specifically, the invention relates to activated clay used for refining aromatic hydrocarbons such as BTX (benzene, toluene, xylene) and the like, and having excellent life and excellent side-reaction-preventing property.
2. (Prior Art)
A solvent extraction method or the like method has heretofore been widely used for separating aromatic hydrocarbons such as benzene, toluene, xylene (C.sub.8 aromatic group) and the like from the starting oils. The recovered aromatic hydrocarbons contain unsaturated compounds such as olefins and diolefins, and a refining treatment (polymerization of ethylenically unsaturated compounds) has been conducted to remove these unsaturated compounds by using the activated clay (Japanese Laid-Open Patent Publication No. 127931/1974).
Japanese Laid-Open Patent Publication No. 263431/1994 discloses a method of producing activated clay for the above-mentioned uses, comprising (a) bringing smectite clay particles into contact with an acid and washing the smectite clay particles with an excess amount of an acid to form the smectite clay particles that are once activated with the acid, (b) mixing the smectite clay particles that are once activated with an acid together with the water and an acid to form the smectite clay particles that are twice activated with the acid, (c) coagulating the smectite clay particles twice activated with the acid so as to form granules in which the smectite clay particles twice activated with the acid are bonded together, and (d) supplying again the granules that were not regenerated into the step of mixing for obtaining a coagulated product having a desired particle size distribution.
The activated clay is used for refining the aromatic hydrocarbons because of the reasons that olefins and diolefins contained in the aromatic hydrocarbons such as BTX are polymerized on the surfaces of the activated clay, and the double bonds decrease due to the polymerization causing the molecular weight to increase such as forming dimers and trimers, enabling them to be easily removed as high-boiling fractions of distillate by distillation. It has been considered that the polymerization takes place since solid acids in the activated clay work as a catalyst.
However, it has been known that the solid acids trigger the polymerization of unsaturated compounds, and further trigger the disproportionation reaction or the isomerization reaction of the alkyl aromatic compounds such as toluene, xylene, etc. It is therefore desired that the activated clay for refining the aromatic hydrocarbons do not cause such side reactions. It is further desired that the activated clay exhibits a long life for the polymerization of unsaturated compounds.
Among the conventional activated clay for treating aromatic hydrocarbons, however, those that exhibit a long life tend to cause side reactions such as disproportionation reaction, and those that little cause side reactions, generally, have a short life. There has not yet been known the activated clay that satisfies both the selectivity of reaction and long life.